1. Field of the Invention
This invention relates to apparatus for purifying water and, more particularly, for purifying rinse water resulting from an impregnation sealing process.
2. Description of the Prior Art
In the quest for lighter, better performing products at less cost, there has been a significant shift in recent years to the use of lighter metals, such as aluminum, in cast sintered form, and in composite materials. Formerly, design engineers specified materials, manufacturing techniques, and heavy casting designs based on the strategy to minimize the problem of porosity, or microporosity. Even microporosity causes air, gas, and hydraulic fluid leakage, creates finishing problems, and, in sintered articles, contributes to machine difficulties. While the former practice kept rejection rates to a minimum, this strategy severely limited design freedom. However, this attitude changed when engineers designing advanced equipment began to exploit the benefits of impregnation sealing. With impregnation sealing, the voids of naturally porous articles are sealed enabling the articles to be used for fluid power components. At the same time, the outer surfaces remain essentially unaffected allowing them to be successfully plated. Today, virtually every manufacturing industry relies heavily on impregnation sealing of porous articles.
The majority of impregnation sealing processes in use today employ self-curing anaerobic sealant materials, that is, materials which cure in the absence of air. Thermal curing sealants are also used, however. These sealant materials, or resins, are customarily a curable composition comprising acrylate monomer and anaerobic or heat cure initiator. Specifics of the chemical compositions and operation of these materials are presented in the co-pending, commonly assigned U.S. patent application Ser. No. (D.D. 87-17) filed concurrently herewith on Jan. 11, 1988 and entitled "Porous Article Impregnation Resin Composition and System for Treating Impregnation Process Waste Water". The processes used for applying the resin require steps of rinsing the article in pure water or in water containing other desirable substances.
In any impregnation sealing process, the aqueous washing of the impregnated articles to remove excess surface sealant or sealant trapped in blind holes results in passage of the excess removed resin into the aqueous washing medium. The anaerobic-cure and/or thermal-cure impregnation resins are substantially insoluble in the aqueous washing medium, resulting in the formation of a dispersion or emulsion of the impregnation resin ("emulsion"). In order to maximize excess sealant removal action in the aqueous rinse step, clean make-up water is introduced to the rinse tank either continuously or in batch fashion, with corresponding discharge of emulsion-containing water from such tank as waste water effluent.
Heretofore, this emulsion-containing waste water effluent of the impregnation process system has either been discharged directly to receiving waters, or else subjected to treatment via conventional biological effluent treatment processes, e.g., activated sludge processing, microbial digestion, and the like.
The monomer utilized in the impregnation sealing process with which the invention is concerned is considered to be nontoxic. Furthermore, although the direct discharge or biological treatment of emulsion-containing waste water from impregnation systems has been generally satisfactory from an environmental standpoint, there is nonetheless a continuing need to improve the effluent quality of discharge streams from such systems, under the impetus of increasing environmental awareness and legislative and regulatory constraints. It has become desirable, then, to reduce or eliminate the emulsion from the rinse water before disposing the rinse water or before reusing it in the process.
Throughout the application, the word "purify" and derivatives thereof used in this regard will be taken to mean the removal of the emulsion or the polymerized material from the rinse water.
Besides concern with the environment, there is an additional concern with present commonly performed disposal of such emulsion containing rinse water directly into either private septic systems or into municipal sewerage systems. Because the impregnant is often an anaerobic resin, it tends to polymerize under water and form on the walls of the discharge piping. This constricts flow of the water and eventually blocks such flow, requiring costly replacement of pipes and associated components and even of an entire septic system in the event its effectiveness becomes compromised.
One publication which is representative of the prior art in this regard is Federal Republic of Germany Offenlegungsschrift 2,705,169 laid open Aug. 10, 1978. This document discloses a process for the treatment of emulsion-like waste waters, which is said to permit practically complete purification. By adding small quantities of heat cure polymerization initiators, the liquid polymerizable substances emulsified in the waste water can be polymerized by heating, or, if accelerators are also added beside the free radical polymerization initiators, even at ambient temperature. The emulsified droplets coalesce to larger drops, which settle very rapidly without use of any other additives, and can easily be separated from the water by screening or filtration. The waste waters treated in this manner may contain, for example, mixtures or solutions of chemical compounds which have homopolymerizable or copolymerizable double bonds in the liquid polyermizable substances. Alpha beta-ethylenically unsaturated polyesters, dissolved in one or more unsaturated copolymerizable monomers, are mentioned as examples.
According to the German reference, after filtration, between 15% and 80% by weight of the polymerizable substance remains following filtration. The present invention is substantially more efficient. An additional drawback of the German reference is the fact that the operating temperatures of the process are 50.degree.-90.degree. C. in one instance and 60.degree.-80.degree. C. in another instance. These are significantly higher than the ambient temperature at which the process of the invention operates. Another significant difference of the present invention resides in the effective use, as disclosed herein and unknown to the German reference, of introducing a photoinitiator to the emulsion containing rinse water, then subjecting it to actinic radiation resulting in polymerization of the emulsion. Another noteworthy publication is Japanese Public Patent Disclosure Bulletin 51-121,159 which discloses a method for treating the eluted waste liquids resulting from the development and, subsequently elution with water, of photosensitive resins. A polymerization initiator is added to the eluted waste liquid of a photosensitive resin and the monomers in the waste liquid are caused to react by applying light or heat to it. Thereafter, cooling and ultrafiltration/concentration are performed whereupon the resulting filtrate can be reused as the eluent of the photosensitive resin while the concentrated liquid is recycled through the ultrafiltration/concentration steps until a sufficiently concentrated liquid, i.e. 10-15 times concentration, is formed. The concentrated liquid is subsequently mixed with oil and subjected to combustion treatment.
While the Japanese reference relates to a batch process, the preferred manner of operation of the present invention is continuous. Furthermore, the operating times recited in the reference are 20 to 40 minutes at elevated temperatures, 60.degree.-95.degree. C., preferably 80.degree.-90.degree. C., and, in an example, recites illumination for a duration of one hour for the effective activation of the photoinitiator. In contrast, the present invention requires less than five minutes to cycle a unit volume of the rinse water at ambient temperatures. Also, the effectiveness reported for the Japanese process is significantly less than the substantially complete removal achieved in the instance of the present invention.